MTHFR C677T DEFECT INCREASES SERUM HOMOCYSTEINE LEVELS AND ENDOTHELIAL PROGENITOR CELL (EPCs) DYSFUNCTION IN ATRIAL FIBRILLATION PATIENTS

Introduction: Hyperhomocysteinemia (HCS) resulting from folate cycle disorders is an independent risk factor for stroke, coronary artery disease and atrial fibrillation (AF) especially during arterial hypertension. Methotrexate (MTX), a chemotherapic and immunosuppressant drug, inhibits several enzymes of the folate cycle and increases serum homocysteine levels. Similarly, patients with genetic MTHFR C677T defects display HCS and increased risk for cardioembolic stroke but it does not explain the complex pathophysiology underlying AF and stroke risk. Interestingly, MTHFR C677T is involved in the hinderance of circulating endothelial progenitor cell (EPCs) functioning, suggesting a one-shot explanation for endothelial dysfunction, atrial stasis and stroke risk. Whether MTX treatment might result in similar cellular changes is unclear. Aim: This study investigates whether in AF patients, a MTHFR C677T mutation would correlate to the degree of atrial fibrosis (AF), homocysteine levels and dysfunctional EPCs. ii) MTX treatment would differentially impair EPCs function in AF patients carrying C677T MTHFR or non-C677T MTHFR isoforms. Methods: We recruited 65 patients subjected to AF ablation, and 30 hypertensive patients as controls. Blood count cell was evaluated at the admission. MTHFR C677T genotypes were elucidated by real-time PCR. Serum homocysteine levels were measured by a commercial laboratory test. EPCs isolation from peripheral blood of all patients and functional analysis in vitro and in vivo were performed in the presence/absence of MTX. Results: Baseline characteristics did not differ between AF patients and controls. The in vitro EPCs migration capacity and the in vivo ability to induce angiogenesis were significantly reduced in AF patients with respect to controls, with a trend to increase in C677T MTHFR vs non-C677T carriers (P<0.007). Interestingly, treatment with MTX (20 μg/mL) in EPCs from non-C677T carriers reproduced the results obtained in EPCs from C677T MTHFR patients both in vitro and in vivo assays. Conclusions: Our current findings support the hypothesis that C677T MTHFR homozygosity promotes folates dysmetabolism, HCS and EPCs diversion, potentially contributing to atrial cardiomyopathy, AF onset and increased stroke risk. MTX treatment dose-dependently induces similar EPCs impairment. Understanding the cumulative impact of folate cycle disruption by MTX and MTHFR mutation might contribute to explain the potential pathogenesis molecular correlation between arterial hypertension and AF.